Problem: Simplify the following expression: $p = \dfrac{1}{2x} + \dfrac{1}{9x}$
Solution: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $2x$ and $9x$ $\lcm(2x, 9x) = 18x$ $ p = \dfrac{9}{9} \cdot \dfrac{1}{2x} + \dfrac{2}{2} \cdot \dfrac{1}{9x} $ $p = \dfrac{9}{18x} + \dfrac{2}{18x}$ $p = \dfrac{9 +2}{18x}$ $p = \dfrac{11}{18x}$